1. Field of the Invention
The present invention relates to a three-dimensional color and shape measuring device for measuring a color and a three-dimensional shape of an object to be measured based on an image signal acquired by picking up an image of the object to be measured by an image pick-up part.
2. Description of the Related Art
Conventionally, there has been known a three-dimensional color and shape measuring device which measures a color and a shape of an object to be measured by picking up an image of the object to be measured in a state that light is projected on the object to be measured, and generates three-dimensional color and shape information of the object to be measured (for example, see JP-A-2003-172610).
The three-dimensional color and shape measuring device includes an image pick-up part having a CCD (Charge Coupled Device) or the like which picks up an image of an object to be measured, a measuring part which includes a computer or the like for measuring a color and a three-dimensional shape of the object to be measured based on an image signal outputted from the image pick-up part after the image pick-up part picks up the object to be measured, and a display part which includes a liquid crystal display panel or the like for displaying a three-dimensional color image of the object to be measured by pasting (texture mapping) an image (a texture) which restores a color of the object to be measured based on a measurement result acquired by the measuring part to a three-dimensional model which restores a three-dimensional shape of the object to be measured based on a measurement result acquired by the measuring part.
Generally, in such a three-dimensional color and shape measuring device, color tone of the three-dimensional color image of the object to be measured displayed on the display part is made to approximate the more real color tone by applying the gray scale correction which conforms to the display characteristic of a display part (herein after referred to as “gamma correction”) to an image signal acquired by picking up an image of the object to be measured by the pickup part.
That is, a display device such as an LCD (Liquid Crystal Device) display or a CRT (Cathode Ray Tube) display possesses a non-linear characteristic in which a gray scale (brightness) of a display image does not exhibit the proportional relationship with a voltage value of an inputted image signal. To be more specific, the display device exhibits the characteristic that a change of brightness is gentle when the input voltage is low and the brightness is sharply changed when the input voltage is high.
Therefore, when an image signal acquired by picking up the object to be measured is directly inputted to the display device by the CCD, an actual color tone of the object to be measured cannot be faithfully reproduced on a display image.
To prevent the occurrence of such a drawback, in the image pick-up part, gamma correction which conforms to the display characteristic of the display device is applied to the image signal acquired by picking up an image of the object to be measured so that the gray scale of the display image exhibits the proportional relationship with the voltage value of the image signal.